The spectral slope \(V_0\)  of the HCN line profiles is very similar to that found for the CO emission from the L1157-B1 outflow cavity (component \(g_2\) ) by [1]}, as indicated by the similarity of the fits and the derived exponent values (\(V_0=4.4\hbox{\hspace{1.99997pt}km\hspace{1.99997pt}s$^{-1}$}\) ). This implies that in the velocity range between \(-20\)  and \(-5\hbox{\hspace{1.99997pt}km\hspace{1.99997pt}s$^{-1}$}\) , both species are probing the same gas component. This is consistent with the analysis of the HCN \(J\) =3–2 spatial distribution obtained with the IRAM 30m telescope at \(9.3\)  (Sect. 4.1) and the HCN \(J\) =1–0 and H\(^{13}\) CN
\(J\) =2–1 with the IRAM interferometer at a few arcsec resolution [2]}, [3]}. As can be seen in Fig. REF , the HNC line profiles look very different from those of HCN in a linear-logarithmic scale. The velocity range of the emission is narrower and stops at \(-10\hbox{\hspace{1.99997pt}km\hspace{1.99997pt}s$^{-1}$}\) , whereas the emission of HCN extends up to \(-30\hbox{\hspace{1.99997pt}km\hspace{1.99997pt}s$^{-1}$}\) . Quantitatively, the HNC line profiles are well fitted by an exponential function \(\exp (-V/V_0)\)  with \(V_0\) = \(2.1\hbox{\hspace{1.99997pt}km\hspace{1.99997pt}s$^{-1}$}\) , i.e. a value of \(V_0\)  half the value obtained for HCN. This supports the idea that HNC and HCN are tracing different regions. We note that the \(V_0\)  value obtained for HNC is actually similar to that found for the CO component \(g_3\)  (\(V_0=2.5\hbox{\hspace{1.99997pt}km\hspace{1.99997pt}s$^{-1}$}\) ), which [1]} showed to be associated with the L1157-B2 outflow cavity.
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